Line both cars up so the batteries are as close as can be. Make sure the cars are in park, are turned off, and not touching each other before you connect the cables. Actually one of them is already off, or you wouldn't be in this predicament right? Make sure all headlights, blinkers, radios and A/C's are off, radar detectors are unplugged, cell phones unplugged, everything off. Jump starting a battery can crank 300+ volts through your system and the transients can destroy equipment.

Familiarize yourself with the Positive (+) and Negative (-) terminals of both batteries so you know exactly which one is which. All batteries are clearly marked so if you can't find it, it's probably under 1/8" of caked on corrosion around the terminals. Wipe off any battery acid that may have leaked.

If the battery is cracked and liquid is leaking out, DO NOT go further! Bite the bullet and go buy another battery and swap it out. If you try to jump start a battery with a crack in it, it will explode, and battery acid will dissolve your eyes (on the positive side though, it does get the red out). It makes no sense to jump a cracked battery, it will die in a few minutes.

Try to clean off any corrosion around the dead battery terminals, and if you have tools, loosen the wires from the terminals, clean them off, then retighten the wires to the shiny posts. Corroded posts prevent the power from getting through the cables and into your battery to revive it.

Usually the positive cable is red or orange, and usually the Negative (-) or ground cable is black.